The present invention relates to safety-belt buckles and, more particularly, those among them intended for automotive vehicles preferably of the land type.
As is known, automotive vehicles, in particular those used on land, are equipped with safety belts which must comply with rigorous specifications generally drawn up, at least in part, by the public authorities.
Under usual conditions, when a safety belt is not acting so as to keep the occupant of a vehicle on his/her seat, as it does in the case of a violent impact, the strap of the belt nomally rests against the body of the person wearing it, if necessary with a very slight tension being exerted by the return mechanism of a winding device. Under such conditions, it is relatively easy to open the buckle of a belt.
Under other circumstances, in particular when a vehicle has turned over following an accident, the strap of the safety belt is subjected to a tension which may be considerably greater; this tension is that which is, for example, exerted by the weight of an occupant who is supported by or suspended from the strap in the event of the vehicle turning over. Under such circumstances, it must be possible for the safety-belt buckle to be opened with relative ease by the occupant him/herself or by another person so that the person thus trapped may be freed. To achieve this is difficult because, in such a situation, the tension of the belt is of the order of approximately 50 daN to 60 daN and it must be possible to open the buckle by exerting a force of 25 daN which, in practice, is extremely difficult to generate.
Moreover, it is essential that, during an actual violent impact, when the safety belt keeps the occupant on his/her seat and its tension exceeds 100 daN for the brief moments when the kinetic energy is absorbed, the locked buckle does not come open at the wrong time or at the critical moment such that it becomes totally ineffective. To achieve this, buckles have been proposed, which, once locked, are kept permanently in this condition.
A safety-belt buckle wth permanent locking is, for example, described in French Patent No. 2,349,296 and its Certificate of Addition No. 2,379,995.
These documents disclose different variations of safety-belt buckles with permanent locking. All the embodiments disclosed therein satisfy the regulations, but their design is somewhat complex. Although such a design does not compromise the reliability of these buckles, it nevertheless means that relatively low manufacturing and assembly costs are difficult to achieve.